• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.4
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• pp.301-307
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• 2013

MRU(motor reduction unit) for KTX is a assembled complex structure that is equipped with a lot of parts at the express train KTX and that is the core power source operating variable speeds. This study is recorded the dynamic characteristics analysis results tested by EMA which is done through the parts and assembly test, transient analysis and stoped train test in order to design the online monitoring system for KTX MRU. And the mode shapes result from critical vibration frequency explain the relation with variable speeds of express train over 250 km/hr. Also these variable speeds make variable operational frequencies at pinion, axle gear mesh frequency and normal bearing fault frequencies. As the specified speed can make resonance with natural frequencies of the MRU, for the train operating stability, this study also presents the MRU's critical speeds calculated by the each train speed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.1
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• pp.119-125
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• 2009

This paper deals with the characteristics of soil ionization affecting the dynamic performance of grounding systems under lightning impulse voltage. A concentric hemispherical electrode system was employed in order to facilitate the field calculation and analysis of the experimental results. The parameters such as the ionization threshold and breakdown field intensity, the pre-ionization and the post ionization resistances, the time-lag to ionization, the transient impedance, the equivalent ionized radius for various soil media were measured and analyzed. The dynamic characteristics of ionization processes under lightning impulse voltage are strongly dependent on the types of soil and water content. As a result, a soil ionization reduces the ground resistance and there is a little effect of applied impulse polarity on the soil ionization threshold field intensity. Although the ionization threshold field intensity of wet clay with 30% water content is the highest, its ionized zone was found to be the smallest amongst the test samples.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.4
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• pp.36-45
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• 2014

Model based control methods are widely used to improve the control performance of diesel engine air systems because the control results of the air system significantly affect the emission level and drivability. However, the model based control algorithm requires a lot of unmeasurable states which are hard to be measured in a mass production engine. In this study, an air system model of the diesel engine is proposed to estimate 11 unmeasurable states using only sensors equipped in a mass production engine. In order to improve the estimation performance in the transient condition, dynamic characteristics of the air system are analyzed and implemented as discrete filters. Turbine and compressor efficiency models are also proposed to overcome a limitation of the constant or look-up table based efficiency values. The proposed air system model was validated in steady state and transient conditions by real-time engine experiments. The maximum error of the estimation for 11 physical states was 11.7%.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.588-592
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• 2002

There was the transient vibration on $H_2$ piping system for cooling the generator in a power plant. We found it was resulted from resonance between the natural vibration of the piping system and exciting force from the turbine rotor by measurement and simulation test. We verified it would be changed the mode shape of the piping system by several simulation test for the structural modification of the piping system. Therefore we concluded that the change of natural vibration mode depends on deeply changing effective length of pipe and reducing supports.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.1000-1007
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• 2007

In this study, structural vibration analyses of a smart unmanned aerial vehicle (UAV) have been conducted considering dynamic hub-loads of tilt rotor. Practical computational structural dynamics technique based on the finite element method is applied using MSC/NASTRAN. The present UAV(TR-S5-04) finite element model is constructed as a full three-dimensional configuration with different fuel conditions and tilting angles for helicopter, transient and airplane flight modes. In addition, the 3-dimensional supporting equipment structures of electronic devices are considered for vibration analysis. As the results of this study, transient structural displacements and accelerations are presented in detail. Moreover, vibration characteristics of structural parts and installed equipments are investigated for different fuel conditions and tilting angles.

• KIEE International Transactions on Power Engineering
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• v.5A no.4
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• pp.366-370
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• 2005

To meet increasing power demand, 500 kV power systems are under consideration in the regions of some Middle Asian countries. As the power system voltage becomes higher, the cost for the power system insulation increases significantly. 500 kV transmission systems will become the basis of a region's power system and they require much higher system reliability. Consequently, by the methods of limiting overvoltages effectively, a reasonable insulation design and coordination must be accomplished. In particular, the Substations must be constructed to be of outdoor type. In order to determine the various factors for the insulation design, the EMTP (Electro-magnetic transient program) is used for the magnification of transient phenomena of the 500 kV systems in the planned network. In this paper, we will explain the calculation results of lightning overvoltages by the EMTP for lightning protection design for the 500 kV substations. To obtain reliable results, the multi-story tower model and EMTP/TACS model are introduced for the simulation of dynamic arc characteristics.

• Proceedings of the KIEE Conference
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• 2001.05a
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• pp.245-247
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• 2001

This paper presents a series of simulation results of transient stability on SCOPF operated power system whose transmission capabilities are limited by voltage stability. Three steps of voltage security guidelines, 5[%], 7[%], 10[%] are introduced to increase power transfer from generation centers to load center and observed the effects of voltage guidelines to transient stability for three kinds of load level(peak, medium, off-peak). As a result, dynamic characteristics weren't affected by the voltage security limits in model system, but became worse for the off-peak level than peak case, and sustain oscillations are observed for the all load level. This gives us some intitutions for the development and applications of security limits to use SCOPF program in open electric market.

• Advances in Energy Research
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• v.2 no.1
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• pp.47-59
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• 2014

Back-to-back STATCOM configuration is an extension of STATCOM in which the reactive power at two-sides and the real power flow through the DC link can be controlled concurrently and independently. This flexible operation brings many advantages to the micro-grids, distributed generation based systems, and deregulated power systems. In this paper, the dynamic control characteristics of the back-to-back STATCOM is investigated by simulating the detailed converter-level model of the converters in PSCAD. Various case studies in a single-machine test system are studied to present that the real power control feature of the BtB-STATCOM, even with a simple controller design, can enhance the transient stability of the machine under different fault scenarios.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.675-680
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• 2004

In this study, a turbine simuiator is designed and manufactured to investigate the transient response of an actual turbine. The rotor mass and bearing stiffness is reduced to 1/140 of its actual turbine. The dynamic characteristics of turbine simulator are similar to those of the actual turbine. The turbine simulator is excited by an electro-magnetic type exciter in the form of half sine wave. Duration time is con☞oiled by Sms, 10ms, and Isms, and maximum acceleration is applied by 3g. Foundation excitation test is performed in stationary condition and rotating condition(6000rpm). The test results can be used to verify the validif of the theoretical afproach for transient analysis of actual turbine.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.1
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• pp.131-138
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• 2010

Because real flow of engine exhaust is very hot and highly transient, it may cause thermal and inertial loads on catalyzed filters in DPF. Transient and detailed flow and thermal simulations are necessary in this field. To assess the importance of time dependent phenomena, typical cone-type configuration such as an underbody DPF is selected for steady and transient analysis. User defined functions of FLUENT by sinusoidal inlet velocities are written and integrated with main solver for realistic simulation. Also, 4-cylinder and 6-cylinder engines for 3,000 L class are considered for the dynamic exhaust effect of engine type. Key parameters to understanding of catalyst performance and durability issues such as flow uniformity index and peak velocity are investigated. Also, pressure drop for engine power are considered. From the simulation results for three different cases, proper approach is recommended.